Semen for artificial insemination is often preserved by freezing. Freezing semen is an effective preservation method, but there is a problem with maintaining potency after thawing. Semen extender compositions are frequently used to preserve the viability of the sperm after thaw.
Many semen extender compositions utilize egg yolk. See, for example, U.S. Pat. No. 6,130,034 to Aitken; U.S. Pat. No. 3,444,039 to Rajamannan; U.S. Pat. No. 3,718,740 to Hafs et al.; and U.S. Pat. No. 3,973,003 to Kolas. A commercial semen extender composition that utilizes raw egg yolk is available under the name Biladyl® from Minitübe GmbH. In general, the egg yolk is added to the composition just prior to the addition of the semen.
Attention has focused on providing sperm extender compositions that do not include egg yolk. For example, see U.S. Pat. No. 6,140,121 to Ellington et al. and European Patent No. EP 685 556.